Hematology equipment is used to analyze the blood of a patient. As with most equipment, it is necessary to calibrate the hematology equipment to obtain accurate tests results. The need to calibrate hematology equipment has become increasingly important due to recent legislative enactments which have required more frequent monitoring of the equipment to ensure proper calibration. The heightened legislative attention to accurate hematology equipment performance is due, no doubt, to the substantial escalation of severe transmittable blood diseases, and in particular, the AIDS virus. The more stringent calibration requirements are therefore certainly prudent, but nevertheless have significantly increased the calibration burden for users of laboratory equipment.
FIG. 1 shows three prior art graphs used for analyzing the operation of a hematology testing device. The graphs of FIG. 1 are commonly referred to as Levey-Jennings plots. As noted at the top of each graph in FIG. 1, each graph depicts data from a particular "assayed range." Depending on the age of the patient, the test results produced by a particular hematology testing device vary significantly in value. A hematology testing device must therefore produce accurate tests results over multiple ranges, and thus, must be calibrated to ensure proper operation over each range.
Referring to FIG. 1(a), the graph depicts the test results of a particular hematology testing device over the "assayed range" of 18 to 24. The various test points, such as point 10, represent particular test results from patient blood analyses taken by a particular hematology device. FIG. 2 shows a table summarizing the results of the data for the graphs of FIG. 1. The mean for the data given in FIG. 1(a) is 20.92 and the standard deviation is 1.13. The table of FIG. 2 also includes data relating to results for a group of hematology devices so that the results of the particular hematology device can be compared to the performance of the group of hematology devices as a whole. The average performance of a group of hematology devices is believed to be an effective method for evaluating the performance of a particular hematology device. If the particular device deviates significantly from the average performance characteristics of the group, this result indicates a problem with the performance of the particular device. Likewise, if the performance of the particular device substantially corresponds with the average performance of the group, this result indicates that the particular device is operating properly and does not require calibration.
The graphs of FIG. 1 have three regions 12, 14, and 16, graphically depicted by shading, and being centered around the line 17 corresponding to the mean for the data of the group of hematology testing devices over the particular level or assayed range. The dark shading indicates data in an unacceptable range; the region without shading indicates data in an acceptable range; and the slightly shaded region indicates data that is borderline, and therefore may or may not be acceptable. The shading is particularly helpful because it provides a readily identifiable visual indicator of the significance of each data point. In short, the graphs of FIG. 1 and the table of FIG. 2 facilitate calibration of a particular hematology testing device. Nevertheless, analyzing the performance of a hematology device required analysis of multiple graphs (i.e., one graph for each data range).
In an effort to allow multiple hematology devices to be analyzed at the same time, another prior art graph was developed (shown in FIG. 3) and is commonly referred to as a Youden Plot. The Youden Plot allows multiple hematology testing devices to be analyzed over two assayed ranges, and was thus a meaningful advance in the art of calibrating hematology testing devices. Referring to FIG. 3, the vertical axis of the graph is centered about the mean of the group data for the assayed range of 18 to 24 (i.e., 21.6), and the horizontal axis is centered about the mean of the group data for the assayed range of 46 to 58 (i.e., 52.9). Point 20 corresponds to the data point for the hematology testing device data from the graphs of FIG. 1(a)&(b) and the table of FIG. 2. The horizontal darkened line 22 corresponds to the mean of the data (i.e., 20.92) of the hematology device over the range of 18 to 24, and the vertical darkened line 24 corresponds to the mean of the data (i.e., 51.92) of the hematology device over the range of 46 to 58. As shown, the data point 20 is in the unshaded region for both the horizontal and vertical axes, and thus demonstrates that the mean for the hematology device over both ranges is acceptable. The remaining data points, such as points 30, 32, and 34, correspond to the mean values of other hematology devices over the ranges of 18 to 24 and 46 to 58.
A significant limitation of the Youden Plot is that only two ranges of data can be analyzed. As explained above, hematology devices operate over multiple ranges to accommodate varying data ranges of blood test results due to such variables as the varying ages of patients. Thus, to completely analyze and calibrate a particular hematology device, several graphs typically must be analyzed. A further limitation of the Youden Plot is that the horizontal and vertical axes are obviously perpendicular, and thus it is very difficult to analyze the linear performance of the hematology device over both ranges depicted on the plot. Each of these limitations are, likewise, common to the Levey-Jennings plots.
While the limitations above have been described in the context of a hematology device, the limitations apply to all devices having multilevel control systems, or stated another way, devices which operate over multiple ranges. The majority of body fluid chemistry analysis devices implement multilevel control systems, and thus suffer from the above-described limitations.